4 replies to this topic

[psycho mini driver]

i own a k&n 57i kit which i have been running in my spi cooper for ages, but lately i have noticed that i am only getting 26 mpg. i do not kno what it was befor i noticed or why i noticed, but i did. so after trying lots, like checking vacume pipes, temp sensor wire....etc i changed my k&n back to the standard air filter box. now,(and i havent yet worked it out) it APPEARS to have settled down and use less petrol. i have also made a radiator cover to keep cold air out as its winter. so, could it be me changing the air filter back to standard which may have improved mpg (which ask the question does it need to be re set up with a k&n) or the fact the engine is getting to opperationg temp now? and help or advise would be appreciated.
thanks,
Adam

[nomininolife]

A bit of a noddy question I know


but how old is the filter and have you cleaned it with the proper stuff and re-oiled it?

[psycho mini driver]

its about a year and a half old, and it was cleaned and reoiled about a month or so ago

[nomininolife]

I would put the filter back on just to see

[Dan]

Yes, it is most likely the air filter which has increased fuel consumption coupled with the cold air. The better air filter allows more air through it, which means it needs to burn more fuel with that air. Also as the air is currently colder than in the summer there is more mass of air being taken in to the engine so again it needs more fuel. Companies don't just fit heated air intakes into the induction system for a laugh, induction temperature control is an important part of tuning. For high power you want lots of cool (not ice cold) air, but for better fuel economy you want only as much mass of air as you need to develop the power required which usually means you don't need it so cool.
The injection computer is programmed to always supply the correct amount of fuel to burn with the mass of air taken in, and makes corrections to the burn based on how much unused oxygen is sensed in the exhaused. It runs slightly richer than carb'd cars do anyway (so is less efficient) as it needs to keep the ratio correct for the cat to deal with.
And yes you should have made the ECU re-calibrate itself to the new air-filter by resetting it. These ECU's are designed to learn as they go so it will eventually set itself up for new filters but it is faster if you reset it yourself and gives better results. It is probably now adapting itself back to the original filter box.
Your engine should reach the correct temperature even on the coldest days, as the thermostat sets the engine temperature. Colder air flowing over the rad just means the 'stat will open less.

Having said all that 26 does seem very low for a relatively standard Mini, so something else may be wrong.